Structural studies on ferritin will be implemented in an effort to understand its functional role of incorporation, retention and subsequent mobilization of iron and its overall function in iron metabolism. Ferritin from various tissues in normal and diseased states will be compared, and elements of structure that are conserved from species to species will be determined. Subunit composition and structure, mechanisms of subunit assembly, and aspects of subunit heterogeneity will be defined. The structural basis for the existence of a family of isoproteins in ferritin from a single tissue will be determined. Methods have been devised to purify and characterize individual isoferritins and the different subunit types found in ferritin. We will also assemble specific combinations of different subunits, to prepare structurally defined apoferritins. The underlying structural basis for the unusual stability of the protein and its resistance to denaturation will be sought. Mechanisms by which iron administration or release to the tissue stimulates ferritin biosynthesis, (thus minimizing toxic effects of iron on the cell) and other regulatory factors involved in the synthesis and turnover of this protein will be explored. We also hope to standardize current assays to monitor tumor patients on the basis of serum ferritin levels, by standard definition of the ferritin antigen systems employed. Ferritin may serve as a model for protein assembly, interactions in non-aqueous media, denaturation of helical domains, and microheterogeneity.